Please post a new thread in the relevant forum for support or if this is a custom or third party style, seek support from the author.
You should see "Tags: Add Tags" in small print directly beneath the thread title on the left side of the page.I must be dense as heck. Where are you clicking to bring up the tag window to apply tags to a thread? I go into a sub forum and I locate a thread I want to tag. I click the thread title to load the thread. Now where do I click?